Equation of a line that has to be tangent

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SUMMARY

The discussion focuses on finding the equation of a line that is tangent to the curve defined by the equation \(y = x^3\) and is parallel to the line represented by \(3x - y - 6 = 0\). The key steps involve determining the gradient of the curve using its derivative, \(y' = 3x^2\), and setting it equal to the slope of the given line, which is 3. Solving the equation \(3x^2 = 3\) yields two solutions for \(x\), confirming the existence of two tangent points. The point-gradient form, \(y - y_1 = m(x - x_1)\), is then used to derive the equations of the tangent lines.

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How would find the equation of a line that has to be tangent to a curve and parallel to another line (i know slope has to be equal)

(you are given the equation of the line and the curve)
x^3
3x-y-6
 
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Ok so you know the gradients have to be the same, so wherever the gradient is 3 on the curve (finding where this happens will be done by using the derivative) will be used to find the equation of the new line.
Taking the derivative of the curve will give you [tex]y'=3x^2[/tex]

and since this has to be equal to the gradient of the line which is 3, just solve [tex]3x^2=3[/tex].
Notice you'll have 2 answers, and that is how it should be! :smile:

And use the point-gradient form for the equation of a line:
[tex]y-y_1=m(x-x_1)[/tex]
 

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